Please note this is just speculation, and I am just interpreting possible evidence.
First of all, lets take you back to update 2.1.0 (Imperial City) that was released a year ago in August/September 2015. A month prior to this, there was some datamining published on elderscrolls.net (
LINK). If you scroll down to the 'Pets' section, you will see some images that look to be in the style of preview images that are used in the Crown Store. But the majority of those pets have only been available before as promo's, like the Bristlegut Piglet for attending events in 2014, and the Imgakin Monkey for participating in the beta. I've always been curious about this, and nothing could really explain these images, until now.
So, with the announcement of Crown Crates, could promo-exclusive collectibles also be available in these crates? Well, if you've played games that have randomised loot boxes similar to this, you usually see an image of the item you've been awarded after opening the box/crate (example: League of Legends
LINK). So what I think is that these Crown Store images will be what is presented to you when you are awarded the corresponding item.
Also, in the past month, the same Rufous Mudcrab pet image datamined a year ago alongside the other collectibles on that webpage has been seen used on the TESOnline Twitter page (
LINK), as well as being featured on the pet code cards distributed to attendees of 2016 conventions. Additionally, the Black Cat pet that was an exclusive promo for those who bought a Japanese edition of ESO from Amazon, has been said to eventually be available for non-Japanese players, as quoted by Gina Bruno:
We do have plans to eventually offer the black cat for non-Japanese players.

Could this be a hint that the Black Cat will be featured in a Crown Crate? After all, the timing of the comment couldn't be any better.
However, whilst some players wanted the Black Cat in the Crown Store, I'm not sure if this is quite what they meant... Maybe even more concerning for some, is that the Dwarven Sphere and High Hrothgar Wraith are featured alongside the promo collectibles, even though they were apart of the Loyalty Program for subscribers.
I'd like to remind everyone again that this is interpretation/speculation after piecing together information I've found, so it is not guaranteed to be true. Likewise with the datamined images; not all are guaranteed to be used.
I've also included a poll with my findings, to see what the general consensus is surrounding if people would be happy seeing promo-exclusive collectibles in Crown Crates, or if they wouldn't like to see them there at all. So, even if you think what I've said is too far-fetched, then it would still be nice to see what people think about the idea of promo-exclusive collectibles being available on the Crown Store.
UPDATE: Gina Bruno confirms that Loyalty Awards will not be available in Crown Crates:
No, Crown Crates will not include the old loyalty rewards.